As a method of evaluating the shape, the size, the quality, and the like of various specimen particles, a method (particle image processing and measuring) is widely used in which the shape, the size, the brightness, and the like of a specimen particle are measured by performing image processing of an image that is acquired by imaging the specimen particle using an imaging device.
As such a particle image processing and measuring method, there is a method in which light is emitted from the upper side or the lower side of a specimen particle using a single illumination device as an illumination device used at the time of photographing, a method in which light is emitted simultaneously from the upper side and the lower side of a specimen particle using a plurality of illumination devices, or a method in which light is emitted from the upper side and the lower side of a specimen particle through independent control processes by independently controlling a plurality of illumination devices.
First, as the method using a single illumination, for example, in Patent Document 1, a method is disclosed in which a specimen particle is sprayed onto a photographing pasteboard that represents a contrast with the specimen particle, and after photographing using reflective light of the illumination that is emitted from the upper side of the specimen particle, particle image processing and measuring is performed. In addition, in Patent Document 2, a reflective plate is arranged on the lower side of a specimen particle, and, after photographing is performed mainly using reflected transmitted light of the illumination that is emitted from the upper side of the specimen particle, particle image processing and measuring is performed. Furthermore, in Patent Document 3, a method is disclosed in which strong light is emitted from the rear face of a dust gathering plate, and, after photographing using light scatted by dusts, particle image processing and measuring is performed.
Next, as the method using simultaneous illumination emitted from the upper side and the lower side of a specimen particle, for example, in Patent Document 4, a method is disclosed, after photographing is performed using light incident from illuminations located on the upper side and the lower side of a micro plate in which a specimen particle is placed, particle image processing and measuring is performed. In addition, in Patent Document 5, a method is disclosed in which an air bubble and a foreign material are discriminated from each other by simultaneously emitting transmitted light and reflected light onto a transparent container. According to the method disclosed in Patent Document 5, an air bubble is recognized as a particle that has high brightness.
Next, as the method using independent illuminations emitted from the upper side and the lower side of a specimen particle, for example, in Patent Document 6, a method is disclosed in which a particle imaging process is performed by emitting transmitted light onto a film, and, after the position of an air bubble within the film is measured, the reflectance of the air bubble is measured by outputting the reflected light, whereby an air bubble and a scratch and a dust are discriminated from each other. In addition, in Patent Document 7, a method is disclosed in which the amount of transmitted light of a particle is measured by emitting transmitted light onto a grain that is a transparent or a semi-transparent particle, and, next, the color of the particle is measured by outputting reflected light, whereby the quality of a fine particle or the like is determined.